The invention relates more particularly to a device for unstacking postal items, such as letters and large-format flat objects or “flats”, in a postal sorting machine, for example.
Patent Document FR 2 797 856 discloses a device for unstacking postal items that is provided with a main magazine 1 having a belt. As shown in FIG. 1, the main magazine 1 comprises, in particular, a motor-driven conveyor belt 2 on which an operator disposes the postal items 3 in a stack and on edge, and a paddle 4 that is also motor-driven, that extends in a substantially vertical plane, and that is moved so as to push the back of the stack in the direction indicated by the arrow 6 facing the unstacking head 5.
The postal items in the stack are held laterally by a jogger edge 7 that extends in a substantially vertical plane along one edge of the conveyor belt 2. The substantially plane unstacking head 5 extends in a vertical plane that is transverse to the direction that is indicated by the arrow 6 and in which the stack of postal items 3 moves on the conveyor belt 2, and said unstacking head is suitable for separating the current first postal item at the front of the stack in the transverse direction indicated by the arrow 8 that is perpendicular to the arrow 6.
The unstacking head 5 is provided with two substantially rectangular openings in which a perforated belt 9 and one or more suction chambers or suction nozzles (not shown) are driven by motors, which openings co-operate to take hold of the first postal item in the stack by suction and to move it in the direction indicated by the arrow 8.
In operation, the stack of postal items 3 disposed in the main magazine 1 is moved by the stepper-type motor-driven drives of the conveyor belt 2 and of the paddle 4, which drives are actuated at the same speed. The first postal item at the front of the stack of postal items is thus brought into abutment against the unstacking head 5 so that that current postal item of the stack is caused to bear against the unstacking head 5 and is separated from the stack by the combined effect of the suction from the nozzles and of the movement of the perforated belt 9. The postal item is then nipped between two deformable wheels 10 disposed in alignment with the head 5. Said wheels 10 are motor-driven so as to propel the current postal item downstream from the unstacker device. They are made of an elastically deformable elastomer material so that they are suitable for adapting to accommodate various thicknesses of postal item.
For the remainder of the sorting process, it is necessary for the postal items to be put into series on exiting from the unstacker device with a constant pitch between consecutive postal items. The drives of the perforated belt 9 and of the suction nozzles are thus actuated and stopped at a constant rate.
That processes of unstacking is repeated as another postal item at the front of the stack is presented facing the unstacking head 5.
In the device of Document FR 2 797 856, the postal items from the stack are put into series continuously, i.e. at a constant unstacking rate.
In general in a postal sorting machine, the postal items exiting from the unstacker are conveyed in series and on edge so as to be taken past a read head. The read head acquires an image of each postal item in the series for the purpose of automatically decoding the inward sorting or outward sorting address of the postal item by means of Optical Character Recognition (OCR) processing. The postal items are then directed to the sorting outlets corresponding to the automatically decoded addresses.
In that type of unstacker device it has been observed that a significant proportion of postal items are not appropriately presented facing the unstacking head while they are being unstacked and might therefore be damaged or torn, e.g. on being engaged by the wheels 10. Such postal items might even cause a jam in the unstacker device, requiring a maintenance operator to take action and the unstacker device to be stopped. Such action is costly and slows down the overall sorting process. Such a situation can be particularly frequent with open postal items of the advertising brochure type or of the magazine type, etc.
Patent Document EP 0 562 954 presents a solution to that problem. In that document, the feed device of the unstacker is similar to the above-described device but further comprises a motor-driven drop-forming feed. The motor-driven drop-forming feed is disposed between the conveyor belt and the unstacking head. The effect of the presence of said motor-driven drop-forming feed is to fan out some of the first postal items (those postal items that are in the drop-forming feed), thereby resulting in the first postal item at the front of the stack being parted from the other postal items and thus finding it easier to be presented appropriately against the unstacking head 5.
In Document EP 0 562 954, presence sensors are provided that are disposed so as to detect a certain inclination of fanning of the postal items in the drop-forming feed and also so as to detect the level of filling of the drop-forming feed. In response to the signals delivered by the sensors, the motor-driven drop-forming feed and/or the conveyor belt are actuated so as to fill the drop-forming feed and/or so as to incline the postal items appropriately.
However, the above-indicated features do not completely eliminate situations in which the postal items are damaged or situations in which a jam forms in the unstacker device, e.g. when very flexible postal items tend to collapse in the drop-forming feed.
Patent Document WO 2005/042386 describes a postal item unstacker device of the “shingler” type that is provided with a main magazine comprising a main conveyor belt and a paddle, and a secondary conveyor belt disposed between the main conveyor belt and the unstacking head. The unstacking head includes a belt having a motor-driven drive that is actuated so as to separate a current first postal item from the stack and so as to eject said postal item in a direction that is transverse to the direction of movement of the postal items. In an unstacker device of the shingler type, the belt of the unstacking head does not co-operate with a suction chamber since the postal items are displaced one on another so as to form a shingle pattern during the unstacking process.
In Document WO 2005/042386, sensors disposed in the unstacking head make it possible to detect the inclination of the current postal item to be unstacked and, in response to the signals delivered by its sensors, the main conveyor belt, the paddle, or the secondary conveyor belt are controlled so as to correct the inclination. In addition, the motor-driven drive of the unstacking head is actuated and stopped in a manner such as to obtain a constant pitch between postal items at the outlet of the unstacker device.
With the device of Document WO 2005/042386, postal item damage situations or jam situations are still too many.
Document US 2002/153654 also discloses a device for unstacking flat objects with presentation control means for controlling how the objects are presented facing an unstacking head, that device being provided with one or two sensors disposed in the unstacking head. Said control means stop the unstacking head when the one or two sensors determine inappropriate presentation of an object. Unstacking of said object is actuated when the presentation of the object becomes appropriate, after the presentation of the object has been corrected. However, with that device, an unacceptable number of postal items are damaged and jam situations are frequent.